In the past, as a magnetic recording medium for audio recording, video recording, and data recording, a magnetic recording medium which is prepared by coating on a non-magnetic support a magnetic coating composition which is obtained by dispersing ferromagnetic particles such as ferromagnetic iron oxide, cobalt-containing iron oxide, chrominum dioxide, ferromagnetic metal particles, etc., into a binder has been widely used.
As a non-magnetic support is mainly used a plastic film such as polyethylene terephalate having high mechanical strength and having excellent solvent resistance. However, a magnetic layer generally has low mechanical strength and poor adhesion to the above-described support, whereby the magnetic layer gradually comes off the support in many cases while the tape is running. In order to overcome this problem, an intermediate layer (or an undercoat layer) is provided between a support and a magnetic layer, as described in U.S. Pat. Nos. 4,504,542 and 4,487,802. Additionally, in order to prevent static electrical charging, addition of carbon black into the intermediate layer has been described in U.S. Pat. Nos. 4,528,240 and 4,617,226.
Polyester is generally used as a binder for the above intermediate layer, but is not satisfactory to provide sufficient adhesive property to the magnetic layer, particularly to a magnetic layer prepared with ferromagnetic metal fine particles. Therefore, when running is repeated, the magnetic layer happens to come off (referred to as powder shedding), resulting in causing an increase of dropouts and clogging of the head gap.